Writing marks a deep divide. In early sociolinguistic work this was very obvious. Basil Bernstein's (1971) distinction between the ‘restricted code’ of working-class speakers and the ‘elaborated code’ of the middle classes mirrored that between spoken vernacular and written language. In largely literate societies, access to written language and the degree of written language skills remain strong indicators of social class, those with no or limited literacy ranging at the bottom of the social hierarchy.

Functional domains of language use are also divided along the oral/literate split, both unwritten languages and illiterate speakers being excluded from the domains of higher communication, such as education, government, and science and technology.

Gender and age, the other social dimensions that have formed the core of sociolinguistic research, likewise correlate with literacy (Stromquist 1999). In Third World countries where illiteracy continues to be a problem, such as India, illiteracy is highest among rural women, as used to be the case in Europe prior to universal education.